Electron discharge device



NOV. 15, 1938. C, F, MlLLER 2,137,005

ELECTRON DISCHARGE DEVICE A original Filed May 28, 1937 Smnentor Gttomeg Patented Nov. 15, 1938 UNITED STATES PATENT OFFICE ELECTRON DISCHARGE DEVICE Original application May 28, 1937, Serial No.

145,198. Divided and this application November 17, 1937, Serial No. 174,981

2 Claims.

This invention relates to electron discharge devices and more especially to radio tubes of the high frequency amplification type.

An object of the invention is to provide an irnproved form of enclosing envelope for a radio tube of the top-cap contact type.

A feature of the invention relates to a radio tube of the top-cap contact type having an outer metal envelope with a reentrant top to shield the top-cap contact electrostatically.

Another feature relates to a radio tube of the top-cap contact type having an outer enclosing metal envelope which is shaped so as to protect the top-cap contact of the tube electrostatically and mechanically.

A further feature relates to an improved structure of a radio tube of the shield-grid type.

A further feature relates to a novel structure of metal envelope radio tube of the shield-grid type.

A still further feature relates to the novel organization, arrangement and disposition of parts which constitute an eflicient radio tube of the shield-grid type.

Other features and advantages not specifically enumerated will be apparent after a consideration of the following detailed descriptions and the appended claims. While the invention will be disclosed in connection with specific types of tubes, it will be understood that this is done merely for purposes of explanation and not by way of limitation. Accordingly, in the drawing,

Fig. 1 shows the invention embodied in a radio tube of the glass-bulb type.

Fig. 2 shows the invention embodied in a radio tube of the metal-bulb type.

Fig, 3 is a modification of Fig. 1.

In certain types of radio tubes, for example those employing a plurality of grids especially tubes of the so-called screen or shield-grid type, it is the usual practice to bring the connection to the control grid out through the top of the tube envelope, and to provide a top-cap for making the external circuit connection thereto. Because of the relatively large surface area of such top-caps, it becomes important in some systems of circuit connections, to reduce the electrostatic pick-up to the top-cap to as low a value as possible. Furthermore, it is desirable to protect the top-cap against blows or jars which would tend to loosen the cap. I have found that by providing a metal enclosing envelope having a reentrant top within which the top-cap of the tube is located, the above and other advantages are achieved.

(.Cl. Z-275) One manner of accomplishing these results is shown in Fig. l. In this figure, the tube proper comprises a glass-enclosing envelope or bulb I which is provided with a suitable base carrying the Contact prongs 2. Suitably mounted within the bulb I is an electrode mount or assembly designated generally by the numeral 3. When this assembly is of the so-called shield or screen-grid type, it is the usual practice to make connection to the control grid through a top-cap 4 which is cemented or otherwise fastened on the top of the bulb I. The lead-in wire 5 is sealed through the wall of the bulb I and connects the control-grid of the electrode assembly with the cap 4. Because of the relatively large surface area of the metal cap 4, it is susceptible to an appreciable electrostatic pick-up. In accordance with the present invention, the glass-bulb I is provided with a metal sheath 6 which preferably closely its the bulb I and is fastened at its lower end to the base of the tube in any convenient manner. For example, the glass-bulb I may be provided at its lower end with a metal cup-shaped member such as described and disclosed in detail in application Serial No. 145,198 and the lower end of sheath 5 may be welded or otherwise fastened to the cylindrical wall of this cup-shaped member.

As shown in Fig. 1, the sheath B extends upwardly beyond the cap 4 for an appreciable distance and is formed with a reentrant portion 'I having a central opening 8 materially larger than the diameter of cap 4, so as to avoid shortcircuiting thereto. If desired an insulator washer or grommet may be provided between the cap 4 and the edge of opening 8 as shown in Fig. 3, although when the sheath 6 is rigidly fastened to the base of the tube as above mentioned, and when it ts the bulb I snugly, such insulating washer may not be necessary. By reason of the upwardly extending reentrant portion of sheath 6, the top-cap 4 is eifectively shielded electrostatically. It will be understood of course that the sheath 6 is connected to ground or some other suitable steady base potential when the tube is connected in circuit so as to effect the necessary electrostatic shielding of the top-cap 4. Because of the reentrant portion l, the top-cap 4 is also to a certain extent protected against blows or jars since it is entirely surrounded by the said reentrant portion l.

Fig. 2 shows the invention embodied in a tube of the metal-bulb type. This tube may be of the conventional metal-tube construction comprising an inverted cup-shaped metal header 9 carrying a plurality of metal eyelets IU within which are sealed the glass beads II, and sealed through the latter are the various lead-in and support Wires for the electrode mount I2. Also fitted and held Within the member 9, is an insulator disc I3 carrying the contact prongs I4. Welded to the header 9 is an evacuated metal-bulb I5 which in accordance with the invention, extends upwardly beyond the mount for an appreciable distance. The lead-in Wire I6 leading for example to the control grid of the mount, is sealed into a glass bead II which in turn is sealed into a metal eyelet I8, a metal contact cap I9 connected to the Wire I6 and is fastened in any suitable manner on the glass-bead II.

The upper end of the metal-bulb I5 is formed with a reentrant portion 20 having an opening at its base into which is sealed, as by welding or brazing, the metal eyelet I8. It will be under stood that the particular method of insulating the lead Wire I6 from the eyelet I8 and the particular manner. of-attaching the cap I9 so that it also is-insulated fromthe said eyelet I8 is merely typical. In this embodiment, When the tube is connected in to circuit, the metal-bulb I5 may be connected to ground thus electrostatically shielding the mount I2 at the same time that it serves as the enclosing envelope for the mount. By reason of the reentrant portion 20, the top-cap I9 is both electrostatically and mechanically protected at all times. While certain specific shapes of tubes have been illustrated herein, it will be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention.

This application is a division of application Serial No. 145,198, filed May 28, 1937.

What I claim is:

1. In combination, a radio tube mount, an enclosing envelope for said mount, a top-cap contact carried by the envelope, and reentrant metal means extending beyond the mount and through which said Contact insulatingly passes, said reentrant means extending upwardly beyond the upper end of said top Contact.

2. In combination, a tube mount, a glass enclosing envelope for said mount, said envelope carrying contact prongs at the lower end, a metal contact cap carried by the upper end of said envelope, and a tubular metal sheath fastened at its lower end to said base and closely fitting said envelope, said sheath having a downwardly reentrant dish-shaped portion through the bottom of which said Contact cap insulatingly passes, said sheath extending upwardly beyond said cap to protect it electrostatically and mechanically.

CARL F. MILLER. 

